Conventional chromatic confocal microscopic system is generally disposed on a desktop for inspecting a surface profile of an object by performing a vertical or translational scanning. Since the conventional chromatic confocal microscopic systems are generally bulky, the space occupied by them may induce inaccessibility or difficulties for in-situ inspection or measurement. Further, if the inclination angle of the object surface is large, or the measurement space is limited, the optical measurement performance achieved by the conventional desktop-type chromatic confocal microscopic system may be significantly limited. For example, if it is required to measure a bump 3-D profile formed on a large-size wafer, due to the limitation of desk-type chromatic confocal microscopic system, it will not be capable for in-situ measurement.
Conventional art, such as US. Pub. No. 2004/0051879, disclosed a confocal displacement sensor for measuring a surface profile of an object. In such art, two measurement beams are created and the intensities of the two measurement beams are recorded by a light detector, respectively. An interpolation between the measured light intensities is performed to determine the profile depth. The height position of the scanned points of the surface can be calculated and the surface of the object can be measured simultaneously at a number of scanning points. Two planar light sources are preferably used for light generation and two planar high-resolution cameras are preferably for light detection.
In addition, U.S. Pat. No. 5,785,651 also disclosed a confocal microscopic apparatus for the quick and accurate determination of surface profile and depth, which comprises a polychromatic light source; a means for focusing the light onto a point of sample target, said means having a known amount of longitudinal chromatic light aberration; and a means for detecting the wavelengths of light reflected from the sample target. The light projected onto the sample target is focused according to wavelength due to the longitudinal chromatic light aberration. While light is reflected based on optical conjugate relationship between the object plane and the imaging plane, the light returning from the sample target is most strongly reflected in a specific wavelength that is focused on a reflective point on the sample, which is then detected through a pinhole locating on the focus plane and is analyzed to determine the surface depth by the means for detecting the wavelength of the reflected light. Furthermore, EP2124085 teaches a slit-scanning confocal microscope, having an illuminating optical system for forming the image of the light source on a sample; and an imaging optical system, which forms an image on line sensor arranged at a position optically conjugated to the light source by reflection light, transmitted light or fluorescence from the sample. The slit-like light source is divided into unit light sources, each of which has a size optically conjugated to a pixel of the line sensor. Moreover, U.S. Pat. No. 7,672,527 also disclosed an apparatus for generating chromatic dispersion through Fresnel lens.
In addition, please refer to the FIG. 1, in the conventional chromatic confocal microscopic system (hereinafter referred to as “conventional system”), a detected light generated by light source 10 is passed through a chromatic dispersion objective 11 and then is projected onto an object 12, thereby forming a reflected light from the object 12. The reflected light is received by a spectrum image sensing unit 13. The optical path of the light in the conventional system is so long (about 320 mm) that the intensity per unit area is reduced. Therefore, the spectrum image sensing unit 13 should have a long-exposure time so as to obtain enough light intensity for effectively performing confocal surface profile measurement. However, extending the exposure time will result in decreasing the measuring speed. In order to achieve high speed in-situ measurement, in the conventional system, it is necessary to arrange a high-power and multi-wavelength light source for increasing the intensity per unit area of light projected onto the object so that the exposure time of the spectrum image sensing unit can be reduced and rapidly acquiring the image associated with the object can be accomplished. However, although the foregoing high-power and multi-wavelength light source can help the conventional system to save exposure time effectively, the cost for making the system is too expensive to be operated practically and efficiently, thereby reducing the competitiveness thereof.